Thermally operated electric switch



March 17, 1 942. .1. E. SHE-RLOCK- THERMALLY OPERA TE D ELECTRIC SWITCH Filed Feb INVENTOR m m S .W w W m M WWW ATTORNEYS Patented Mar. 17, 1942 THERMALLY OPERATED ELECTRIC SWITCH John Edward Sherlock, Sunbury-on-Thames, England Application February 17, 1940, Serial No. 319,520 In Great Britain February 20, 1939 1 Claim.

This invention relates to thermally operated electrical switch devices and has for its object to provide an improved construction or arrangement thereof designed to enable the making or breaking of engagement of the contact members to be effected by a snap action and to avoid the disadvantage of a decrease in pressure on the contact members prior to the moment of breaking contact.

According to the invention a thermally operated electrica1 switch device is provided comprising a member having a double ramp thereon, a spring pressed component engaging said member and a thermostatic control element adapted to cause movement of the double ramp member or the spring pressed component whereby the recoil of the spring or springs compressed by the action of the first portion of the ramp is converted by the action of the second portion of the ramp into a sudden movement or snap action to open or close electrical contact elements.

According to one form of the invention a thermally operated electrical switch device is provided comprising a thermostatic control element adapted to cause movement of a spindle having a double ramp formed thereon and a movable switch contact carrying member having elements in spring pressed engagement with said spindle and so arranged that the recoil of a spring compressed by the action of the first part of the ramp is converted by the action of the second part of the ramp into a sudden movement of the said contact carrying member to open or close the switch.

According to another form of the invention a thermally operated electrical switch device is provided comprising fixed and movable contact members, a thermostatic control element adapted to operate the movable contact member by a snap action to open or close the switch and means associated with the operating mechanism to cause the pressure on the contact members to increase up to the moment of breaking contact.

Reference will now be made to the accompanying drawing which illustrates by way of example a temperature sensitive electrical switch constructed according to the invention and in which- Fig. 1 is a sectional plan and Fig. 2 is a section taken on the line A-B of Fig. 1.

In the construction illustrated the control part consists of a slidable push rod a guided in a casing b and bearing at one end against a flexible metal bellows c and at the other end against a disc or plate 11 supporting a control spring e the pressure of which can be adjusted by means of a regulating screw I mounted co-axially with the push rod a and carrying a collar g bearing upon one end of the spring e, the said collar being prevented from turning by engagement with a rod h.

Mounted round the push rod a is a snap action unit comprising a plate 1' supporting a housing 7 in which three plungers is set at angles of apart are arranged so that they press radially inwards (as shown in Fig. 2) against a double ramp 1 formed on the push rod (1. The plungers k are pressed inwards by a common spring in the form of an endless tension spring m passing round all the plungers and bearing directly upon their outer ends. The double ramp consists of two frustoconical surfaces set base to base so as to provide a ridge at the point of transition from one surface to the other as shown in Fig. l. The aforesaid plate i may be guided by the push rod or by a part of the casing, but it is preferred to provide an odd number of spring-pressed plungers, say three as shown and to leave sufficient clearance between the plate 1 and the push rod a and surrounding parts to prevent any contact of the plate i with parts which might exert a frictional drag during the snap-action movement.

The movement of the aforesaid plate 1' is limited in one direction by the engagement of a number of electrical contacts 12 on one face of the plate with fixed contacts 0 mounted in an annular flange p in the casing and in the other direction by a stop which may consist of a flanged sleeve q slidably mounted in the casing co-axially with the push rod. The sleeve q is controlled by a screw r accessible from the forward end s of the casing for the purpose of displacing the sleeve and thus adjusting the differential of the instrument.

Any number of electrical contacts may be operated by the device but it is preferred to provide three contacts so as to ensure that all contacts can be closed simultaneously in spite of slight inaccuracies of adjustment of the fixed contacts 0 which might involve a slight tilting of the plate 1'. If two contacts only are desired, suitable stops may be provided to limit the tilting movement of the plate 1 about a line joining the two contacts proper. For a three phase switch in which three pairs of contacts may be required to be bridged simultaneously by three pairs of contacts on the plate z, the members of each pair of fixed contacts may be set close together so that the contact between the six fixed contacts and the plate 1' approximates to a three point contact.

The adjusting screw 1 which controls the pressure of the control spring 2 is operated by a hand wheel or knob 15 associated with a graduated scale. In order to provide for easy setting or alteration of the temperature range of the instrument the hand wheel t is attached to a sleeve u coupled to the adjusting screw f by means of a friction clutch 1) which can be released by pressing the screw 1 axially inwards against the pressure of the control spring 6. The hand wheel t is attached to the sleeve u by means of an axial screw w which engages directly in the end of the adjusting screw and clamps the adjusting screw 1, the sleeve u and hand wheel t securely together. The said axial screw to is accessible from the front of the hand wheel 75 and its removal permits the hand wheel to be detached so that access can be gained to the end of the adjusting screw f by means of a screw driver or other tool for causing a screw a: mounted within the adjusting screw to be caused to project more or less beyond the inner end of the adjusting screw for the purpose of adjusting the range of the instrument.

In order to provide for a definite 01f position independent of the temperature control, the aforesaid sleeve u may carry a cam or ramp 1/ adapted to co-operate with a part fixed to the casing and arranged to push the sleeve u inwards through a sufficient distance to cause the inner end of the adjusting screw 1 or a screw in to abut against the push rod 01. and to move the same to the off position. This mechanism is arranged to come into action only when the hand wheel t is rotated to an extreme position.

In the operation of the device above described, 1

expansion of the bellows 0 causes gradual movement of the push rod on so that the springpressed plungers 7c ride up the ramp Z and by their outward movement increase the tension of the spring 112 controlling them. When a certain temperature is reached, the plungers reach the ridge and as soon as this point is passed the' spring 172 recoils and causes the plate 2' to move suddenly with a snap action so that the switch contacts n and 0 are closed. On subsequent contraction of the bellows c the spring m is again gradually loaded this time by the part of the ramp which previously produced the sudden movement, and when the ridge is again passed a snap action movement occurs by which the contacts are suddenly separated. During the preliminary spring loading phase, the pressure on the electric contacts gradually increases so that gradual relaxation of contact pressure prior to the break is avoided.

By the arrangement above described the sudden movement of the plate 1 to make or break contact takes place in a direction opposite to that of the control member or push rod a so that the difierential of the instrument is directly dependent upon the range of movement of the plate 1'. This differential is adjustable by varying the position of the sleeve q or of the fixed contact members I.

It is to be understood that various modifications can be made in the arrangement above described without departing from the invention. For example, instead of operating the spindle a from the bellows c, the snap action unit carried by the plate 2' could be operated by the bellows and the spindle a in such case utilised to operate the switch.

I claim:

A thermally operated electrical switch device, comprising a thermostatic control element, a spindle responsive to the movements of said element, a double conical ramp formed on said spindle, a housing, fixed electrical switch contact elements within said housing, a ring freely mounted around said spindle, a plurality of plungers equidistantly spaced around and movable radially within said ring, spring means maintaining the inner ends of said plungers in contact with one or the other of the coned surfaces of said ramp and guiding said ring for movement axially of said spindle, movable electrical switch contact elements carried by said ring and movable thereby into and out of operative engagement with said fixed contacts, and means for varying the extent of movement of said ring in the direction which disengages said contacts to thereby adjust the temperature differential of the device.

JOHN EDWARD SHERLOCK. 

